1. Field of the Invention
The present invention relates to the stabilization of organic substrate materials to light and more particularly to the stabilization of organic compounds, particularly organic dyestuffs, to light.
2. Discussion of the Prior Art
In general, organic substrate materials, for instance, organic dyestuffs, tend to fade or to discolor upon exposure to light. A number of studies on the prevention of such fading or discoloration of organic dyestuffs, i.e., on improving light fastness, have been carried out in related technical fields including ink manufacture, textile dyeing, color photography and the like. The present invention is an effective method of improving the light fastness of organic substrate materials.
In the present specification, the term "organic substrate material" or "substrate material" includes substances which appear colored or colorless to the human eye under exposure to sunlight, that is, they include not only substances having absorption maxima in the visible region but also substances having absorption maxima in the near ultraviolet region, e.g., optical brightening agents, and further, substances having absorption maxima in the infrared region. Namely, in the present invention, organic substrate materials include organic substances having absorption maxima in the wavelength region of about 300 nm in the ultraviolet region to about 800 nm in infrared region.
These organic substrate materials occur particularly in photographic materials, e.g., color films, prints, diffusion transfer units, etc., in colored polymers useful as an agricultural vinyl cover sheets, umbrellas, tents, etc., fluorescent whitening agents, and dyed textiles, etc., and this invention is directed to improving the light fastness of these materials in each of these fileds.
The term "dye" or "dyestuff" in the present specification includes an organic compound which appears colored to the human eye under exposure to sunlight.
The term "light" in the present specification includes electromagnetic radiation of wavelengths under about 800 nm, that is, it includes ultraviolet radiation under about 400 nm, visible light of about 400 nm to about 700 nm and infrared radiation of about 700 nm to about 800 nm.
The tendency for organic substrate materials, for instance, dyes or dyestuffs, to fade or to discolor upon optical exposure has long been known, and various methods for reducing fading or discoloration, that is, for improving the light fastness, have been proposed. For example, the fastness of an organic compound such as an indophenol, an indoaniline, an azo, an azomethine or like dyestuff to visible and ultraviolet light can be improved by mixing it with a phenolic compound having a fused heterocyclic system, as described in U.S. Pat. No. 3,432,300.
In the art of silver halide photographic light-sensitive materials, the oxidation products of an aromatic primary amine developing agent react with a color coupler to give rise to azomethine dyes or indoaniline dyes as described in C. E. K. Mees & T. H. James, The Theory of the Photographic Process, Chapter 17, Macmillan, New York (1967). A number of methods for improving the stability of images made up by such dyes, that is, color photographic images, are known. For example, the use of hydroquinone derivatives as fading or discoloration inhibitors as reported in U.S. Pat. Nos. 2,360,290, 2,418,613, 2,675,314, 2,701,197, 2,704,713, 2,728,659, 2,732,300, 2,735,765, 2,710,801 and 2,816,028, British Pat. No. 1,363,921, etc., the use of gallic acid derivatives as reported in U.S. Pat. Nos. 3,457,079 and 3,069,262, Japanese Patent Publication No. 13,496/68, etc., the use of p-alkoxyphenols as reported in U.S. Pat. Nos. 2,735,765 and 3,698,909, and the use of derivatives of chroman, coumaran and the like as reported in U.S. Pat. Nos. 3,432,300, 3,573,050, 3,574,627, 3,764,337, 3,574,626, 3,698,909 and 4,015,990, have been proposed. However, these derivatives do not effect sufficient fade or discoloration prevention.
In addition, another method in which the stability of organic substrate materials to light is improved by using azomethine quenching compounds having an absorption maxima in a wavelength region shifted to longer wavelengths than the absorption maxima of the substrate materials has been proposed in British Pat. No. 1,451,000. However, this method also suffers a disadvantage that the azomethine quenching compounds are per se intensely colored and, consequently, largely affect the hue of the substrate materials.
Moreover, by analogy to the prevention of photo-deterioration of polymers utilizing metal complexes, as described in J. P. Guillory & R. S. Becker, J. Polym. Sci., Polym. Chem. Ed., 12, 993 (1974) and R. P. R. Ranaweera & G. Scott, J. Polym. Sci., Polym. Lett. Ed., 13, 71 (1975), still another method in which dyestuffs are stabilized by the addition of metal complexes has been reported in Japanese Patent Application (OPI) No. 87,649/75 (The term "OPI" as used herein refers to a "published unexamined Japanese patent application") and Research Disclosure, 15162 (1976). However, these complexes in themselves do not have a large fade preventing effect and additionally, they do not have a high solubility in common organic solvents. Therefore, they cannot be added in amounts necessary to exhibit a sufficient fade prevention effect. In addition, since these complexes per se are intensely colored, they suffer the disadvantage that their addition in large amounts adversely affects the color hue and the purity of the organic substrate materials and particularly dyestuffs.